epithelium

epithelium

[ep″ĭ-the´le-um] (pl. epithe´lia) (Gr.)

the cellular covering of internal and external surfaces of the body, including the lining of vessels and other small cavities. It consists of cells joined by small amounts of cementing substances. Epithelium is classified into types on the basis of the number of layers deep and the shape of the superficial cells.

transitional epithelium a type characteristically found lining hollow organs, such as the urinary bladder, that are subject to great mechanical change due to contraction and distention; originally thought to represent a transition between stratified squamous and columnar epithelium.

ep·i·the·li·um

, pl.

ep·i·the·li·a

(ep'i-thē'lē-ŭm, -ă), [TA]

The purely cellular avascular layer covering all free surfaces, cutaneous, mucous, and serous, including the glands and other structures derived therefrom.

[G. epi, upon, + thēlē, nipple, a term applied originally to the thin skin covering the nipples and the papillary layer of the border of the lips]

epithelium

/ep·i·the·li·um/ (-the´le-um) pl. epithe´lia [Gr.] the cellular covering of internal and external body surfaces, including the lining of vessels and small cavities. It consists of cells joined by small amounts of cementing substances and is classified according to the number of layers and the shape of the cells.

transitional epithelium that characteristically found lining hollow organs that are subject to great mechanical change due to contraction and distention; originally thought to represent a transition between stratified squamous and columnar epithelium.

epithelium

(ĕp′ə-thē′lē-əm)

n.pl.epithe·lia(-lē-ə) or epithe·liums

Membranous tissue composed of one or more layers of cells separated by very little intercellular substance and forming the covering of most internal and external surfaces of the body and its organs.

ep′i·the′li·al adj.

epithelium

[-thē′lē·əm]

Etymology: Gk, epi + thele, nipple

the covering of the internal and external organs of the body and the lining of vessels, body cavities, glands, and organs. It consists of cells bound together by connective material and varies in the number of layers and the kinds of cells. The stratified squamous epithelium of the epidermis comprises five different cellular layers. epithelial,adj.

Classification of epithelium

ep·i·the·li·um

, pl. epithelia (ep'i-thē'lē-ŭm, -ă) [TA]

The purely cellular avascular layer covering all the free surfaces, cutaneous, mucous, and serous, including the glands and other structures derived therefrom.

[G. epi, upon, + thēlē, nipple, a term applied originally to the thin skin covering the nipples and the papillary layer of the border of the lips]

epithelium

The layer of cells forming the epidermis of the skin and the surface layer of mucous and serous membranes. The cells rest on a basement membrane and lie in close approximation with little intercellular material between them. They are devoid of blood vessels. The epithelium may be simple, consisting of a single layer, or stratified, consisting of several layers. Cells making up the epithelium may be flat (squamous), cube-shaped (cuboidal), or cylindrical (columnar). Modified forms of epithelium include ciliated, pseudostratified, glandular, and neuroepithelium. The epithelium may include goblet cells, which secrete mucus. Stratified squamous epithelium may be keratinized for a protective function or abnormally keratinized in pathological response. Squamous epithelium is classified as endothelium, which lines the blood vessels and the heart, and mesothelium, which lines the serous cavities. Epithelium serves the general functions of protection, absorption, and secretion, and specialized functions such as movement of substances through ducts, production of germ cells, and reception of stimuli. Its ability to regenerate is excellent; it may replace itself as frequently as every 24 hr. See: illustration; skinepithelial (-al), adjective

ciliated epithelium

Epithelium with hairlike processes on the surface that wave actively only in one direction. This type is present in the respiratory tract and fallopian tubes.

columnar epithelium

Epithelium composed of cylindrical cells.

cuboidal epithelium

Epithelium consisting of cube-shaped or prismatic cells with height about equal to their width.

germinal epithelium

1. Epithelium that covers the surface of the genital ridge of the urogenital folds of an embryo. It gives rise to the seminiferous tubules of the testes and the surface layer of the ovary. It was once thought to produce the germ cells (spermatozoa and ova).

2. The epithelium that covers the surface of a mature mammalian ovary.

glandular epithelium

Epithelium consisting of secretory cells.

junctional epithelium

A band of nonkeratinized stratified squamous epithelium that attaches both to the gingiva (on one side) and the crown of the tooth (on the other). Synonym: epithelial attachment; gingival cuff

laminated epithelium

mesenchymal epithelium

Squamous epithelium that lines the subarachnoid and subdural cavities, the chambers of the eye, and the perilymphatic spaces of the ear.

pavement epithelium

Epithelium consisting of flat, platelike cells in a single layer.

pigmented epithelium

Epithelium containing pigment granules.

pseudostratified epithelium

Epithelium in which the bases of cells rest on the basement membrane but the distal ends of some do not reach the surface. Their nuclei lie at different levels, giving the appearance of stratification.

reduced enamel epithelium

Combined epithelial layers of the enamel organ, which form a protective layer over the enamel crown as it erupts and then become the primary epithelial attachment surrounding the tooth.

squamous epithelium

The flat form of epithelial cells.

stratified epithelium

Epithelium with the cells in layers; mitosis takes place in the lowest layer. Synonym: laminated epithelium

sulcular epithelium

The nonkeratinized epithelium that lines the gingival sulcus.

transitional epithelium

A form of stratified epithelium in which the cuboidal cells adjust to mechanical changes such as stretching and recoiling. This type of tissue is found only in the urinary system (renal pelvis, ureter, bladder, and a part of the urethra).

epithelium

The non-stick coating cell layer for all surfaces of the body except the insides of blood and lymph vessels. Epithelium may be single-layered, or ‘stratified’ and in several layers, with the cells becoming flatter and more scaly towards the surface, as in the skin. It may be covered with fine wafting hair-like structures (cilia), as in the respiratory tract, and it may contain mucus-secreting ‘goblet’ cells. See also ENDOTHELIUM and EPIDERMIS.

Fig. 153 Epithelium (1) . Types of epithelium.

epithelium

(in animals) a layer of covering cells lying on a basement membrane that is called simple epithelium when one cell thick and compound epithelium when several cells thick, and usually covers connective tissue embryologically derived from the ECTODERM. The cells sometimes have a secretory function and are held together by a cementing substance to form a sheet. Their shape gives rise to names descriptive of the cells, e.g. columnar, cubical, squamous (see Fig. 153 ). Where the epithelium is more than one cell thick it is described as stratified. Similar cells can be derived from MESODERM and are referred to as mesothelium when lining the COELOM, and as ENDOTHELIUM when lining blood vessels.

(dez´mosōmz´), n an electronmicroscopic finding of intercellular bridges that serve to attach adjacent epithelial cells to each other.

epithelium, enamel, inner,

n the innermost layer of cells (ameloblasts) of the enamel organ that deposit the organic matrix of the enamel on the crown of the developing tooth. Also the innermost layer of Hertwig's epithelial root sheath.

epithelium, enamel, outer,

n the outermost layer of cells of the enamel organ. It is separated from the inner enamel epithelium in the area of the developing crown by the stratum intermedium and stellate reticulum and lies immediately adjacent to the inner enamel epithelium in the area of the developing root.

epithelium, enamel, reduced,

n combined enamel epithelium; the remains of the enamel organ after enamel formation is complete. After eruption of the tip of the crown, that part of the combined epithelium remaining on the enamel surface is called the epithelial attachment.

epithelium, gingival,

n a stratified squamous epithelium consisting of a basal layer; it is keratinized or parakeratinized.

epithelium, hyperplastic,

n an increase in thickness, with alterations in structure, produced by proliferation of cellular elements of epithelium.

epithelium, oral,

n the epithelial covering of the oral mucosa. Composed of stratified squamous epithelium of varying thickness and varying degrees of keratinization.

epithelium, pocket,

n the epithelium that lines the periodontal pocket. Its most prominent characteristics are the presence of hyperplasia and ulceration.

epithelium, pseudostratified

(soo´dōstrat´ifīd), n a type of epithelium in which there appears to be several layers (or strata) of cells, but all cells actually are resting on the base layer. Often ciliated and occurs only in mucosa.

epithelium, squamous

n a type of epithelium consisting of flat, scalelike cells.

epithelium, stratified squamous,

n the variety of epithelium covering the oral mucosa and dermal surfaces; composed of layers of cells oriented parallel to the surface. The various layers of cells in order from basement membrane to surface are stratum germinativum, stratum spinosum (prickle cell layer), and stratum lucidum (in dermal epithelium). The gingival epithelium generally exhibits some degree of keratinization, variable from parakeratinization to orthokeratinization within the layers of the stratum granulosum (granular layer) and stratum corneum (keratin layer).

epithelium, sulcal,

n the stratified squamous epithelium forming the covering of the soft tissue wall of the gingival sulcus, or crevice. Extends from the gingival margin to the line of attachment of the epithelium to the tooth surface.

epithelium

pl. epithelia [Gr.] the cellular covering of internal and external surfaces of the body, including the lining of vessels and other small cavities. It consists of cells joined by small amounts of cementing substances. Epithelium is classified into types on the basis of the number of layers deep and the shape of the superficial cells. Standard classifications include ciliated (cilia attached), columnar (taller than wide), cuboidal (same height as width), pseudostratified (single layer but because of varying cell height appears to be more than one), simple (one cell layer), squamous (flattened, plate-like cells), stratified (more than one layer), transitional (variable number of layers apparent). Other types are listed below.

anterior epithelium

the thin layer of stratified squamous cells that form the outermost layer of the cornea.

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